A pile driver drives a post into the ground. The mass of the pile driver is 2800

Question

A pile driver drives a post into the ground. The mass of the pile driver is 2800 kg and it is dropped through a height of 7.0 m on each stroke. If the resisting force of the ground is 5 times 10^6 N. how far is the post driven in on each stroke? 3.8 cm 0.4 cm 0 cm 96 cm 4.8 cm In a two-body collision, if the kinetic energy of the system is conserved, then which of the following best describes the momentum after the collision? must be less must also be conserved may also be conserved is doubled in value A 6-kg object is moving to the right at 4 m/s and collides with a 4-kg object moving to the left at 6 m/s. The objects collide and stick together. After the collision, the combined object: has the same kinetic energy that the system had before the collision. has more kinetic energy than the system had before the collision. has no kinetic energy. has less momentum than the system had before the collision. An amount of work equal to 3.0 J is required to compress the spring in a spring-gun What is the "launch speed" of a 15 g marble? 14 m/s 15 m/s 18 m/s 20 m/s Constants: G = 6.67 times l0^-11 N m^2/kg^2 e- = l.60 times l0^-19 C M_E = 5.98 times 10^24 kg k = 8.99 times 10^9 Nm^2/C^2 mo_0 = 1.26 times 10^-6 T-m/A C_0 = 8.85 times 10^-12 C^2/N-m^2 R_E = 6.38 times 10^6 m

Explanation / Answer

a) work done = loss in potential energy

F*d=mgh

so d=mgh/F = 2800*9.8*7/5*10^6 = 3.8 cm

b) momentum is always conserved

c) Total momentum befor collission = 6*4-4*6 = 0

So final momentum =0 so kinetic energy =0

d) 1/2 mV^2= 3

so v = (3*2/15*10^-3)^1/2 = 20 m/s

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